1. Field of Invention
The present invention relates to a method for preparing a low k material and a film thereof, and more particularly to a method for preparing a low k material of silicon oxide containing a large amount of fluorocarbon and a film thereof. The method is applicable to a low k material in an ultra-large-scale-integration (ULSI) circuit manufacturing process and a preparation method thereof.
2. Related Art
In recent years, designers and manufacturers of large-scale-integration (LSI) circuits have continuously designed and manufactured micro scale devices, for the purpose of increasing a package density of a semiconductor chip, improving a work speed of a component, and adding relevant functions. Therefore, after a gate length of a transistor is reduced to less than 0.13 um, the number and density of interconnections on each chip of an ultra-large-scale-integration (ULSI) circuit are greatly increased. When interconnected wires between the chips, including the inter-layer and intra-layer interconnected wires, become smaller and are spaced more compactly, a small conductor volume will increase resistivity (R) of the metal wire, and smaller inter-wire and inter-layer intervals will increase a capacitance (C) between the wires. An RC delay caused by the R and C becomes an increasing part in an overall signal delay of a circuit, neutralizing any speed advantage resulting from the small device size. Therefore, the use and development of a low R metal (such as copper) will continuously reduce the R of the interconnected wires. On the other hand, capacitance can be reduced using a dielectric material with a low k. Fluorine-doped silicon oxide film is a low k film.
Current fluorine-doped silicon oxide film is generally fabricated using tetraethoxysilane (TEOS) and silane as precursors, and adding a CnF2n+2 or a SinF2+2 gas as a source of fluorine into a plasma enhanced chemical vapor deposition (PECVD) manufacturing process, in which the source for deposition of fluorocarbon needs two or more precursors. It is disclosed in a literature such as [Low Dielectric Constant Interlayer Using Fluorinated-Doped Silicon Oxide, Jpn. J. Appl. Phys. 33, 408 (1994).] published by Usami et al. that C2F6 gas is added into TEOS/O2 to form a low k material. In addition, [Reduction Mechanism in the Dielectric Constant of Fluorine-Doped Silicon Dioxide Films, J. Electrochem. Soc. 144, 2531 (1997)] published by Lim et al. discloses that CF4 is added into SiH4/N2O to form a low k material. Moreover, [Structure and Chemical Composition of Fluorinated SiO2 Film Deposited Using SiF4/O2 Plasma, J. Vac. Sci. Technol. A15, 2893 (1997)] published by Han et al. discloses that SiF4 is added into a SiH4/O2 system to form a low k material. These low k materials containing fluorocarbon all require two or more precursors to act as the source for the deposition of fluorocarbon.
Since SiF4 gas is hard to dissociate, a dual frequency plasma enhanced chemical vapor deposition (DF-PECVD) method or a electron cyclotron resonance chemical vapor deposition (ECRCVD) method are usually employed in the industry to enhance the dissociation of the gas material, and a ratio of unstable Si—F2 bonds in the film is lowered through ion bombardment on a surface of the film. However, these two equipment systems disclosed are very costly, and are therefore inappropriate for mass production in commercial applications.
U.S. Pat. No. 7,611,996 entitled “Multi-stage curing of low K nano-porous films” discloses a thermal treatment method for adjusting, for example, heat resistance and water resistance of a low k film. However, the patent does not disclose a best structural composition of the low k material film that may contain fluorocarbon long chains and a corresponding thermal treatment method.
Furthermore, U.S. Pat. No. 7,618,889 entitled “Dual damascene fabrication with low k materials” discloses a method for preparing a low k material, but does not disclose in detail a composition and a post-treatment method for improving the heat resistance and water resistance of the low k material.
To overcome the disadvantages described previously, the applicants invent, through careful researches and experiments, a method for preparing a low k material of silicon dioxide containing fluorocarbon and a film thereof. U.S. Pat. Nos. 7,611,996 and 7,618,889 are used as cited references in the present invention.